Ron Natalie wrote:

Well the octane numbers aren't directly comparable. The major reason you
can run 100LL is because your aircraft was originally certificated for 80 or
100 octane Avgas. The STC doesn't undo the original certification, just adds
the option of of using autogas.

While what Ron writes (above) is true, it isn't directly on point because of thread drift. The
originator specifically said "auto engines in homebuilts". * Unless the homebuilder (or
firewall-forward packager) has done womething *really* strange, the only problem with using
Aviation 100LL in an auto engine is the lead in 100LL: it *may* foul the plugs, poison the O2
sensor (if engine has one), and sludge the oil (depending on the oil type).

Russell Kent

(*) Shaddup BOb. :-)